Process and apparatus for producing organic polysulfides

ABSTRACT

A filtering means containing gelatinous and solid materials is cleaned without dismantling the filtering means by contacting the gelatinous material inside the filtering means with a solvent, thereby physically degrading the gelatinous material such that the degraded gelatinous material can pass through the filtering means.

This application is a division of application Ser. No. 09/587,918, filedJun. 6, 2000, now, U.S. Pat. No. 6,284,926.

The present invention relates to an improved process and apparatus forproducing organic polysulfides. More particularly, the present inventionrelates to an improved process and apparatus for removing undesirablebyproducts from a crude organic polysulfide product.

BACKGROUND OF THE INVENTION

Organic polysulfides are useful for many purposes such as additives forelastomers, antioxidants for lubricating oils, intermediates for theproduction of organic chemicals, insecticides, and germicides andadditives for diesel fuels to improve cetane number and ignitionqualities. Organic polysulfides are also useful in the compounding ofhigh pressure lubricants and in the acceleration of rubber treatingprocesses.

It is known that organic polysulfides can be produced by reactingmercaptans with elemental sulfur in the presence of a basic catalyst.The crude organic polysulfide product produced by such a reactiontypically comprises a distribution of various organic polysulfides (forexample, disulfides, trisulfides, and tetrasulfides), hydrogen sulfide,at least one solid byproduct, and at least one gelatinous byproduct.Generally, the crude organic polysulfide product is further processed toobtain a purified organic polysulfide product.

One process employed to obtain a purified organic polysulfide product isthe removal of the solid and gelatinous byproducts from the crudeorganic polysulfide product. The solid and gelatinous byproducts aretypically removed by passing the crude organic polysulfide productthrough a filter. Due to the buildup of solid and gelatinous byproductswithin the filter, such filter must be cleaned periodically.

The cleaning of the byproduct filter is a labor intensive operationwherein the filter assembly is dismantled and the filtered byproductsare manually removed. In addition, such manual cleaning of the filter isan unpleasant task due to the foul order of the filtered byproducts.Thus, it is desirable to develop an apparatus and process for producinga purified organic polysulfide product which substantially decreases thefrequency of required manual cleanings of the byproduct filter.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved process andapparatus for producing organic polysulfides.

Another object of the present invention is to provide an improvedprocess and apparatus for removing solid and gelatinous byproducts froma crude organic polysulfide product.

A further object of the present invention is to provide a process andapparatus which substantially decreases the frequency of required manualcleanings of a filter which removes solid and gelatinous byproducts froma crude organic polysulfide product.

Other objects and advantages of the present invention will become moreapparent as the invention is more fully disclosed hereinbelow.

According to an embodiment of the present invention, a process isprovided comprising the steps of (a) trapping at least one solidmaterial and at least one gelatinous material in a filtering means, (b)contacting the gelatinous material with a solvent to produce a degradedgelatinous material capable of passing through the filtering means, and(c) passing the degraded gelatinous material through the filteringmeans.

According to a further embodiment of the present invention, an apparatusis provided which comprises (a) a filtering means, (b) a solvent sourceconnected with the filtering means, and (c) a solvent flow control meansfor controlling the flow of a solvent between the solvent source and thefiltering means.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a simplified flow diagram of an apparatus and process forproducing organic polysulfides in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

It has been discovered that the efficiency of a process for producingorganic polysulfides by reacting a mercaptan and a sulfur compound inthe presence of a catalyst can be improved by employing a novel methodof cleaning the filtering means which traps solid and gelatinousmaterials present in the crude organic polysulfide product.

The mercaptan suitable for use as a reactant in such a process ofproducing a crude organic polysulfide product can be any mercaptanhaving the formula RSH, wherein R is a hydrocarbyl radical having 1 toabout 30, preferably 1 to about 20, and most preferably 2 to 15 carbonatoms. The hydrocarbyl radical can be linear or branched and can bealkyl, aryl, cycloalkyl, alkylaryl, aralkyl, alkenyl radicals, orcombinations of two or more thereof. Preferably, the hydrocarbyl radicalis an alkyl radical. Presently preferred mercaptans are tertiarymercaptans. The presently most preferred mercaptan is t-butyl mercaptan.

The sulfur compound suitable for use as a reactant in the presentprocess can be any sulfur-containing compound capable of reacting with amercaptan to produce a crude organic polysulfide product. Preferably,the sulfur compound is elemental sulfur. The amount of sulfur compoundcontacted with the mercaptan depends on the desired sulfur content andthe organic polysulfide product. For an average sulfur content of qsulfurs per polysulfide molecule (q−1) moles of sulfur must be added per2 moles of mercaptan and 1 mole of hydrogen sulfide will be produced per2 moles of mercaptans reacted. It is, however, preferred that about 0.5to about 10, preferably about 1 to about 5, and most preferably 1.0 to2.0 moles of mercaptan per mole of sulfur is used.

The catalyst suitable for use in the present process can be any catalystcapable of catalyzing the reaction of a mercaptan and a sulfur compoundto form a crude organic polysulfide product. The presently preferredcatalyst comprises a basic catalyst which can be an inorganic base, anorganic base, or combinations of two ore more thereof. Suitable organicbases include, but are not limited to tetramethylammonium hydroxide,tetraethylammonium hydroxide, tetrapropylammonium hydroxide,tetramethylammonium bisulfide, tetraethylammonium bisulfide,trimethylamine, triethylamine, n-butylamine and combinations of two ormore thereof. Suitable inorganic bases include, but are not limited to,lithium hydroxide, sodium hydroxide, sodium bisulfide, potassiumhydroxide, calcium hydroxide, magnesium hydroxide, sodium bicarbonate,sodium carbonate, sodium oxide, sodium sulfide, magnesium oxide, calciumoxide, calcium carbonate, sodium phenoxide, barium phenoxide, calciumphenoxide, R₁ONa, R₁SNa, and combinations of any two or more thereof;where R₁ is a C₁-C₁₈ alkyl radical, or combinations of any two or morethereof. Presently, the amine catalysts are not as preferred as othercatalysts, and an inorganic base is preferred because of theavailability and low cost of inorganic bases. Among the inorganic bases,sodium hydroxide is preferred.

The catalyst useful in the process of the present invention can furthercomprise a surfactant, preferably an alkoxylated compound, mostpreferably an alkoxylated alcohol. An alkoxylated alcohol useful in thepresent invention has a general formula of R₂O[CH₂CH(R₃)O]_(m)H where R₂is a C₁-C₂₀ hydrocarbyl radical selected from the group consisting ofalkyl radical, alkylaryl radical, aryl radical, cycloalkyl radical, andalkenyl radical. Preferably, R₂ is a C₆-C₁₈ alkyl radical. Mostpreferably, R₂ is a C₁₀-C₁₆ alkyl radical. Preferably, R₃ is selectedfrom the group consisting of hydrogen, C₁-C₁₆ alkyl radical and C₂-C₁₆alkenyl radicals. More preferably, R₃ is a hydrogen or a C₁-C₃ alkylradical. Most preferably, R₃ is hydrogen. Preferably, m is a number from1 to about 20, more preferably from about 2 to about 12, and mostpreferably from 5 to 10. An example of a suitable alkoxylated alcohol isTERGITOL® 15-S-7 which is an ethoxylated alcohol, manufactured andmarketed by Union Carbide Corporation. Other suitable alkoxylatedalcohols are also available from Union Carbide Corporation.

The weight ratio of base to surfactant in the catalyst can vary widelyso long as the ratio can catalyze the reaction of a mercaptan and asulfur compound. Preferably, the weight ratio of a base to surfactant isfrom about 10:1 to about 1:100, more preferably from about 2:1 to about1:10, most preferably from 1:1 to 1:5.

The amount of catalyst contacted with the mercaptan and sulfur compoundcan be any amount capable of catalyzing the formation of a crude organicpolysulfide product. The weight of the catalyst as a percentage of theweight of mercaptans can be in the range of from about 0.001 to about 10percent, preferably from about 0.01 to about 3 percent, and mostpreferably from 0.05 to 2 percent.

The contacting of the mercaptan, sulfur compound, and catalyst can takeplace in any suitable reaction vessel. The contacting is generallyaccomplished by slowly adding one of the reactants to a mixture of theother reactant and the catalyst. The reaction of the mercaptan andsulfur compound can commence at ambient temperatures, but is generallydesirable to accelerate the reaction by stirring and/or increasing thetemperature of the liquid reaction solution. The reaction temperaturecan be from about 30° C. to about 250° C., preferably from about 50° C.to about 150° C., more preferable from about 80° C. to about 130° C.,and most preferably from 95° C. to 115° C. The reaction pressure canvary widely from about 1 atmosphere to about 20 atmospheres, preferablyfrom about 1 atmosphere to about 10 atmospheres. The period of timerequired to produce a suitable crude organic polysulfide product isgenerally from about 0.5 hours to about 20 hours, more preferably fromabout 1 hour to about 10 hours, and most preferably from about 2 hoursto about 5 hours.

The crude organic polysulfide product produced by the above-describedreaction of the mercaptan and sulfur compound comprises at least oneorganic polysulfide, hydrogen sulfide, at least one gelatinousbyproduct, and at least one solid byproduct.

The organic polysulfides of the crude organic polysulfide product can beany organic polysulfides having the formula of RS_(x)R, wherein each Rcan be the same or different and are each a hydrocarbyl radical having 1to about 30, preferably 1 to about 20, and most preferably 2 to about 15carbon atoms, and x is a number from 2 to 10, preferably 2 to 6, andmost preferably 3 to 5. The hydrocarbyl radical can be linear orbranched and can be alkyl, aryl, cycloalkyl, alkylaryl, aralkyl, alkenylradicals, or combinations of two or more thereof. Preferably, thehydrocarbyl radical is an alkyl radical. Preferred organic polysulfidesare di-t-butyl polysulfides. More preferred organic polysulfides includedi-t-butyl disulfide, di-t-butyl trisulfide, and di-t-butyltetrasulfide. The most preferred organic polysulfide is di-t-butyltrisulfide.

The gelatinous byproduct of the crude organic polysufide product cancomprise any material or combination of materials having a gelatinousphysical nature. The gelatinous byproduct typically comprises a quantityof the surfactant employed in the mercaptan/sulfur reaction as well assmall quantities of organic polysulfide compounds.

The solid byproduct of the crude organic polysulfide product can be anysolid material or combination of solid materials. Sodium bicarbonate isan example of a common solid material that can be present in a crudeorganic polysulfide product. Unreacted sulfur compound is a furtherexample of a solid material that can be present in a crude organicpolysulfide product.

Subsequent to the above-described reaction, the crude organicpolysulfide product can be subjected to a variety of purification,separation, recovery, and stabilization methods to produce a purifiedorganic polysulfide product. A purification process of particularimportance in the present invention involves the removal of at least onegelatinous byproduct and at least one solid byproduct from the crudeorganic polysulfide product.

The removal of the gelatinous and solid byproducts can be accomplishedby passing the crude organic polysulfide product through a filteringmeans. The filtering means can be any filtering means known in the artwhich is capable of trapping at least a portion of the gelatinous andsolid byproducts without trapping more than in insignificant amount ofthe organic polysulfides. The filtering means preferably comprises atleast one filter. More preferably, the filtering means comprises atleast one filter having a filtration rating of from about 0.1 microns toabout 40 microns. Most preferably, the filtering means comprises twofilters, each having a filtration rating of from 0.5 to 10 microns.

One problem associated with using a filtering means to remove thegelatinous and solid byproducts from the crude organic polysulfideproduct is that flow through the filtering means can rapidly becomeobstructed by the mixture of the gelatinous byproduct and solidbyproduct trapped within the filtering means. In order to detect whenthe filtering means contains too much trapped byproduct, the pressuredrop across the filtering means can be measured during flow of the crudeorganic polysulfide product through the filtering means. A low pressuredrop indicates a relative clean (i.e., free of trapped byproducts)filtering means, while a high pressure drop indicates a relativelyplugged filtering means.

When the pressure drop across the filtering means is undesirably high,the filtering means contains too much filtered byproduct and must becleaned or replaced. The value of the undesirably high pressure drop canvary depending on the maximum differential pressure rating of thefiltering means and various preferred operating conditions. Typically,an undesirably high pressure drop is from 50 percent to 100 percent ofthe maximum differential pressure recommended by the manufacturer of thefiltering means.

It has been discovered that when the pressure drop across the filteringmeans becomes undesirably high, it is advantageous to remove thegelatinous byproduct from the filtering means without manuallydisassembling the filter. The removal of the gelatinous byproduct can beaccomplished by contacting the gelatinous byproduct with a solvent,thereby physically degrading the gelatinous byproduct such that thedegraded gelatinous byproduct can pass through the filtering means.

Any solvent capable of physically degrading the gelatinous byproduct canbe employed in the inventive process. Preferably, the solvent is anorganic solvent. Examples of organic solvents are aromatic hydrocarbonssuch as benzene, toluene, xylene, and ethylbenzene; aliphatichydrocarbons such as pentane, hexane, heptane, and octane; alicyclichydrocarbons such as cyclohexane and methylcyclohexane; halogenatedhydrocarbons such as chloroform, dichloromethane, dichloroethane,chlorobenzene, chlorobutane, bromoform, and bromobenzene; alcohols suchas methanol, ethanol, 2-propanol, and t-butanol; ketones such asacetone, methyl ethyl ketone, and isobutyl methyl ketone; ethers such asdiethyl ether, diisopropyl ether, dibutyl ether, ethylene glycoldimethyl ether, dioxane, and tetrahydrofuran; esters such as ethylacetate; nitrites such as acetonitrile; and aprotic polar solvents suchas sulfur-containing compounds [e.g., sulfoxides (e.g., dimethylsulfoxide), sulfones (e.g., sulfolane)], N,N-dimethylformamide, anddimethyl sulfoxide. More preferably, the solvent is a ketone. Mostpreferably, the solvent is acetone.

Prior to contacting the gelatinous byproduct with the solvent, it ispreferred to terminate the charging of the crude organic polysulfide tothe portion of the filtering means being cleaned with solvent. Thegelatinous byproduct within the filtering means can be contacted withthe solvent using any suitable method known in the art. The solvent maybe contacted with the gelatinous byproduct by conducting the solventfrom a solvent source through the filtering means. Preferably, thesolvent is circulated by a pump from a solvent tank, through thefiltering means, and back to the solvent tank in a closed-loop solventflow system.

The solvent is contacted with the gelatinous byproduct in the filteringmeans at a rate and for a time period suitable to remove substantiallyall gelatinous byproduct from the filtering means. Preferably, thecontacting of the solvent with the gelatinous byproduct in the filtercontinues for a period necessary to restore an adequately low pressuredrop across the filtering means when the charging of the crude organicpolysulfide product to the filtering means is resumed. An adequately lowpressure drop is a pressure drop that is less than the undesirably highpressure drop, described above. Preferably, the adequately low pressuredrop is less than 95 percent of the undesirably high pressure drop, morepreferably less than 80 percent, and most preferably less than 50percent.

When the pressure drop across the filtering means is adequately low, asufficient amount of gelatinous byproduct has been removed from thefiltering means and the charging of the solvent to the filtering meanscan be terminated. Thereafter, the filtering means can be dried byremoving residual solvent from the filtering means, in order to preventcontamination of the crude organic polysulfide product with the solvent.Drying of the filtering means can be accomplished using any suitablemeans known in the art, for example, by purging the filtering means witha suitable drying gas, such as, for example, oxygen and/or nitrogen.

If the contacting of the solvent with the gelatinous material in thefiltering means does not provide an adequately low pressure drop, thefiltering means is plugged with the solid byproduct and must be manuallycleaned or replaced.

Removing the gelatinous byproduct without removing the solid byproductfrom the filtering means, in accordance with the present invention,decreases the frequency of required manual cleanings of the filteringmeans. In addition, because the foul odor generally associated withremoving a gelatinous and solid byproduct mixture from the filteringmeans is caused by the gelatinous byproduct, the manual removal of onlythe solid byproduct, in accordance with the present invention, isrelatively odor-free.

Referring now to FIG. 1. In accordance with an embodiment of the presentinvention, a mercaptan, sulfur compound, and catalyst are charged to areactor 4 via a conduit 2. The crude organic polysulfide productproduced by the reaction in reactor 4 is conducted from reactor 4 to athree-way valve 8 via a conduit 6. Upstream three-way valve 8 controlsthe flow of the crude organic polysulfide product to either a conduit 10or a conduit 12.

The system depicted in FIG. 1 comprises two filters—a filter 14 and afilter 16. Filter 14 and filter 16 are capable of trapping at least aportion of the solid and gelatinous byproducts contained in the crudeorganic polysulfide product while allowing at least a portion, andpreferably substantially all, of the organic polysulfides to passtherethrough. The use of two filters allows for the continuous filteringof the crude organic polysulfide product by allowing one filter to becleaned while the other filter is receiving the crude organicpolysulfide product.

The filtered organic polysulfide product exits filter 14 or filter 16,whichever is receiving the crude organic polysulfide product, into aconduit 18 or a conduit 20. From conduit 18 or conduit 20, the filteredorganic polysulfide product is sent to storage or further processing viaa three-way valve 22 and a conduit 24.

The cleaning of the filter not receiving the crude organic polysulfideproduct is accomplished by contacting the contents of such filter with asolvent 30. Solvent 30 is conducted to the filter not receiving crudeorganic polysulfide product by switching on a pump 36, thereby causingsolvent 30 to flow from a solvent tank 32 to the filter not receivingcrude organic polysulfide product via a conduit 34, pump 36, a conduit38, three-way valve 40, and a header 44. The flow of solvent 30 througheither filter 14 or filter 16 is controlled by adjusting a valve 46, avalve 48, a valve 50, and a valve 52. After passing through the filternot receiving crude organic polysulfide product, solvent 30 is returnedto solvent tank 32 via header 54, a three-way valve 56, and a conduit60. The circulation of solvent 30 from solvent tank 32 to the filter notreceiving the crude organic polysulfide product is continued until suchfilter is cleaned of substantially all trapped gelatinous byproduct.Thereafter, pump 36 is turned off, and residual solvent 30 is removedfrom the filter not receiving the crude organic polysulfide product bypurging with nitrogen.

The process of purging the filter with nitrogen is commenced byadjusting a three-way valve 40 and a three-way valve 56 to allownitrogen to flow to the filter not receiving the crude organicpolysulfide product via a conduit 42, three-way valve 40, and header 44.The flow of nitrogen to either filter 14 or filter 16 is controlled byvalve 46, valve 48, valve 50, and valve 52. After flowing through thefilter not receiving the crude organic polysulfide product, the nitrogenis sent to a flare via header 54, three-way valve 56, and a conduit 58.

After being cleaned and purged, the filter not receiving the crudeorganic polysulfide product is ready to receive the crude organicpolysulfide product.

To determine when the flow of the crude organic polysulfide productshould be switched from one filter to the other, the pressure dropacross the filter is measured using an upstream pressure gauge 26 and adownstream pressure gauge 28. When the pressure drop across the filterreceiving the crude organic polysulfide product is undesirably high(i.e., the filter is plugged), three-way valve 8 and three-way valve 22are adjusted to cause the crude organic polysulfide product to flowthrough the non-plugged filter. Once flow is diverted to the non-pluggedfilter, the plugged filter can be cleaned in accordance with theabove-described process.

The above described filtering, cleaning, and purging process is repeateduntil the cleaning of filter 14 or filter 16 with solvent 30 no longerprovides an adequately low pressure drop across the filter, therebyindicating that the filter is plugged with solid byproduct. At thatpoint, all flow to the plugged filter is terminated, the plugged filteris dismantled, and the byproducts located therein are removed. After thebyproducts are removed, the manually cleaned filter is reassembled, andcharging of the crude organic polysulfide product to the manuallycleaned filter is resumed.

The following examples are provided to further illustrate the practiceof the present invention and are not intended to limit the scope of theinvention of the claims.

EXAMPLE I

The following example demonstrates a conventional method of preparingorganic polysulfides by reacting a mercaptan and a sulfur compound inthe presence of a basic catalyst and, thereafter, removing a gelatinousbyproduct and a solid byproduct from the crude organic polysulfideproduct.

In a batch reaction process, a crude organic polysulfide was produced byreacting about 585 pounds of t-butyl mercaptan and about 135 pounds offlour sulfur in the presence of about 200 grams of 50% sodium hydroxideand about 200 grams of TERGITOL® 15-S-7 ethoxylated alcohol (UnionCarbide Corporation; Danbury, Conn.). The reaction took place in a 100gallon Hastelloy C reactor.

During the reaction, the reactor contents were stirred. Reactionconditions included a reaction temperature of about 105° C. and areaction pressure which varied from about 0 psig to about 135 psig dueto the buildup and venting of hydrogen sulfide. The reaction period wasapproximately 3 hours.

After the reaction period, the crude organic polysulfide product waspassed through a Cuno model CT101 filter housing containing a 5 micronCuno model DPPTB1 filter cartridge (Cuno Incorporated; Meriden, Conn.).The pressure drop across the filter was monitored as the crude organicpolysulfide product flowed through the filter. When the pressure dropacross the filter was 30 psi, flow of the crude organic polysulfideproduct to the filter was terminated. The filter was disassembled, thefilter contents were manually removed, and a foul odor associated withthe filter contents was detected.

The filter contents were weighed. The total weight of the filtercontents was 160 grams, with 40 grams being attributable to a byproductof gelatinous nature, and 120 grams being attributable to a byproductwhich was solid in nature.

EXAMPLE II

The following example demonstrates the inventive method of preparingorganic polysulfides by reacting a mercaptan and sulfur in the presenceof a basic catalyst, and thereafter passing the crude organicpolysulfide product through a filter which was cleaned by contacting itscontents with a solvent.

The crude organic polysulfide product employed in the present examplewas produced using substantially the same process described in ExampleI.

As in Example I, the crude organic polysulfide product was passedthrough a Cuno model CT101 filter housing containing a 5 micron Cunomodel DPPTB1 filter cartridge, having a 30 psi maximum pressuredifferential. When the pressure drop across the filter was about 30 psi,the flow of the crude organic polysulfide product was terminated, butthe filter was not disassembled. Rather, acetone was circulated throughthe filter by charging a tank with 65 pounds of acetone, pumping acetoneto the filter inlet, and returning the acetone to the tank in aclosed-loop flow system. Acetone was allowed to circulate through thesystem for about 20 minutes. The acetone pump was then turned off andresidual acetone was removed from the filtering means by purging withnitrogen. Flow of the crude organic polysulfide product through thefiltering system was then resumed.

The process of (1) charging the crude organic polysulfide product to thefilter, (2) monitoring of the pressure drop, (3) cleaning of thefiltering system with acetone, and (4) purging with nitrogen wasrepeated until the filter was sufficiently full of solid byproducts suchthat the acetone cleaning was ineffective to restore an adequately lowpressure drop (less than about 25 psi) across the filter. At that point,the filter was disassembled, and the filter contents were manuallyremoved. No foul odor was detected with the filter contents.

The filter contents were weighed. The total weight of the filtercontents was 760 grams, all of which was attributable to byproductswhich were solid in nature.

The inventive method of Example II allowed for the time between manualcleanings of the filter to be extended by approximately six-fold overthe conventional process of Example I, because the filter cleaned by theinventive process was able to trap 760 grams of solid byproduct prior toa required manual cleaning, while the filter cleaned by the conventionalmethod was only able to trap 120 grams of solid byproduct prior to arequired manual cleaning. In addition, there was no foul odor associatedwith manually cleaning the filter which had been cleaned in accordancewith the inventive process.

While this invention has been described in detail for the purpose ofillustration, it should not be construed as limited thereby but intendedto cover all changes and modifications within the spirit and scopethereof.

That which is claimed is:
 1. A process comprising: (a) trapping at leastone solid material comprising sodium bicarbonate and at least onegelatinous material comprising organic polysulfide in a filtering means;(b) contacting said at least one gelatinous material with a solvent toproduce a degraded gelatinous material capable of passing through saidfiltering means; and (c) passing said degraded gelatinous materialthrough said filtering means.
 2. A process according to claim 1, whereinsaid at least one gelatinous material comprises a surfactant.
 3. Aprocess according to claim 2 wherein said solvent is an organic solvent.4. A process according to claim 3 wherein said filtering means comprisesat least one filter.
 5. A process according to claim 4 wherein said atleast one solid material further comprises a sulfur compound.
 6. Aprocess according to claim 5 wherein said solvent is selected from thegroup consisting of aromatic hydrocarbons, aliphatic hydrocarbons,alicyclic hydrocarbons, halogenated hydrocarbons, alcohols, ketones,ethers, esters, and aprotic polar solvents.
 7. A process according toclaim 6 wherein said filtering means comprises at least one filterhaving a filtration rating of from about 0.1 microns to about 40microns.
 8. A process according to claim 6 wherein said solventcomprises a ketone.
 9. A process according to claim 8 wherein saidfiltering means comprises two filters, each having a filtration ratingof from 0.5 microns to 20 microns.